Pornography triggers brain activity in people with compulsive sexual behavior – sex addiction – similar to that triggered by drugs in the brains of drug addicts, according to new paper.

Some psychologists claim up to 4 percent of adults is affected by compulsive sexual behavior, an obsession with sexual thoughts, feelings or behavior which they are unable to control. This is different than the usual level of sexual thinking, called 'being a man'.

Like any compulsion, it can have an impact on a person's personal life and work, leading to significant distress and feelings of shame. Excessive use of pornography is one of the main features identified in many people with compulsive sexual behavior, but because there is little belief it is a real thing, there is no definition for the condition.

Scholars from the Department of Psychiatry at the University of Cambridge looked at brain activity in 19 male patients claiming sex addiction and compared them to the same number of healthy volunteers. The patients said they started watching pornography at earlier ages and in higher proportions relative to the healthy volunteers.

Participants were shown a series of short videos featuring either sexually explicit content or sports while brain activity was monitored using functional magnetic resonance imaging (fMRI), which uses a blood oxygen level dependent (BOLD) signal to measure brain activity.

The coronal view shows the age covariate for explicit videos in subjects with Compulsive Sexual Behaviors (CSB) with a healthy volunteer (HV) exclusive mask. The graph shows the corresponding regression analysis for the ventral striatal parameter estimate (PE) and age in years. The image is shown as a region of interest at P<0.005.10.1371/journal.pone.0102419

The researchers found that three regions in particular were more active in the brains of the people with sex addiction compared with the healthy volunteers. Significantly, these regions – the ventral striatum, dorsal anterior cingulate and amygdala – were regions that are also particularly activated in drug addicts when shown drug stimuli. The ventral striatum is involved in processing reward and motivation, whilst the dorsal anterior cingulate is implicated in anticipating rewards and drug craving. The amygdala is involved in processing the significance of events and emotions.

The researchers also asked the participants to rate the level of sexual desire that they felt while watching the videos, and how much they liked the videos. Drug addicts are thought to be driven to seek their drug because they want it rather than enjoy and this incentive motivation is a popular hypothesis in addiction disorders.

As expected, patients with compulsive sexual behavior showed higher levels of desire towards the sexually explicit videos, but did not necessarily rate them higher on liking scores.Desire was also correlated with higher interactions between regions within the network identified – greater cross-talk between the dorsal cingulate, ventral striatum and amygdala – for explicit compared to sports videos.

They also found a correlation between brain activity and age – the younger the patient, the greater the level of activity in the ventral striatum in response to pornography. The association was strongest in individuals with compulsive sexual behavior. The frontal control regions of the brain – considered the 'brakes' on our compulsivity – continue to develop into the mid-twenties and this imbalance may account for greater impulsivity and risk taking behaviors in younger people. The age-related findings in individuals with compulsive sexual behaviors suggest that the ventral striatum may be important in developmental aspects of sex addiction in a similar fashion as it is in drug addictions, although direct testing of this possibility is needed.

"There are clear differences in brain activity between patients who have compulsive sexual behavior and healthy volunteers. These differences mirror those of drug addicts," says Dr. Valerie Voon, a Wellcome Trust Intermediate Clinical Fellow at the University of Cambridge. "Whilst these findings are interesting, it's important to note, however, that they could not be used to diagnose the condition. Nor does our research necessarily provide evidence that these individuals are addicted to porn – or that porn is inherently addictive. Much more research is required to understand this relationship between compulsive sexual behavior and drug addiction."